Lithuania’s nuclear regulator, VATESI, has granted a positive safety statement on the Constor RBMK1500/M2 containers, supplied by Germany’s GNS, and intended for storage of used nuclear fuel from the two RBMK reactors at Ignalina, which is now being decommissioned.

In total, some 18,000 used assemblies will have to be appropriately placed into casks and stored in a new facility being built by a consortium of GNS and Russia’s Nukem Technologies.

“VATESI agreed to the modification of the engineering design of the container related to physical properties of the shielding material (Constorit)," the statement says. In mid-2011, when the customer reviewed the manufacturing documents, some cask parameters were found to be non-compliant, specifically with respect to the design and structural material specifications, project and preliminary safety analysis report. Constorit is a steel shielding material consisting of iron aggregate frame and hardened cement paste, which is hermetically encapsulated between the inner and outer steel liner.

GNS undertook some additional calculations and modelling of Constorit behaviour with changed properties under different operating conditions. An additional analysis of the container safety was carried out jointly with Ignalina NPP. According to Ignalina NPP director general Darius Janulevičius, the container safety and its fitness for long-term storage of used fuel must be finally confirmed by hot tests, which are scheduled for August 2016-January 2017.